Air conditioner and method for operating same

ABSTRACT

An air conditioner according to the present comprises a plurality of chillers which include a compressor, a condenser, a expansion device and an evaporator and supply cold water through water pipes connected to the evaporator in parallel. An operating chiller of the plurality of chillers sets a cold water set temperature of the operating chiller according to pressure difference between high pressure part and low pressure part and controls the compressor capacity according to the cold water set temperature and transmits an operation order to a chiller not operating until the present if the pressure difference is more than the set pressure for the set time and at least one of the chillers is not operating. Thus, it is possible to perform an efficient operation according to load and to minimized power consumption.

TECHNICAL FIELD

The present invention relates to an air conditioner and operation method of the same, more particularly, to an air conditioner and the operation method of the same which cools water by a refrigeration cycle and performs heat exchange between an air and the cooled water and supplies the air to an indoor space.

BACKGROUND ART

Generally, an air conditioner is an appliance, which cools or heats an indoor space by using a refrigeration cycle of a refrigerant comprising a compressor, a condenser, an expansion device and an evaporator to offer a pleasant indoor environment to users.

The air conditioner comprises an evaporator, which performs heat exchange between water and a refrigerant, and a heat exchanger such as a coil of cold water in which the water cooled by the heat exchange cools an air, so that the cold air cooled by the heat exchanger blows to the indoor space and can cool the indoor space.

In the conventional air conditioner, if the air conditioner operates, a compressor operates, and if the air conditioner stops, the compressor stops. When the compressor operates, the cold water can cool an air and the air can cool the indoor space. If the temperature of the cold water is not appropriately changed according to the cooling load of the indoor space, the air conditioner is difficult to operate by optimum efficiency and to respond to the partial load effectively.

DISCLOSURE Technical Problem

Accordingly, the present invention is directed to an air conditioner and operation method of the same that substantially obviate one or more problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide an air conditioner, which can control a compressor by setting set temperature of cold water according to pressure difference of a refrigeration cycle.

Another object of the present invention is to provide an operation method of the air conditioner which can improve the efficiency by operating some of chillers in case of the partial load in the air conditioning area or can quickly respond to the load by adding a spare chiller in case of big load.

Technical Solution

To achieve these objects and other advantages and in accordance with the purpose of the invention, there is provided an air conditioner comprising: a plurality of chillers which include a compressor, a condenser, a expansion device and an evaporator and supply cold water through water pipes connected to the evaporator in parallel, wherein an operating chiller of the plurality of chillers sets a cold water set temperature of the operating chiller according to pressure difference between high pressure part and low pressure part and controls the compressor capacity according to the cold water set temperature and transmits an operation order to a chiller not operating until the present if the pressure difference is more than the set pressure for the set time and at least one of the chillers is not operating.

Each of the chillers may comprise a low pressure sensor for sensing suction pressure of the compressor; and a high pressure sensor for sensing discharge pressure of the compressor; and a chiller controller for setting a cold water set temperature according to the pressure difference between the high pressure sensed by the high pressure sensor and the low pressure sensed by the low pressure sensor, and for controlling the compressor capacity according to the cold water set temperature.

The air conditioner comprises a common water pipe temperature sensor for sensing temperature of a common water pipe which coolant supplied from the plurality of the chillers passes through together, the chiller controller may set a cold water set temperature according to the temperature sensed by the common water pipe temperature sensor.

The air conditioner may further comprise a communication line, which is connected to each the chiller controllers of the chillers for transmitting an operation order from one of the chillers to the other.

In another aspect of the present invention, there is provided an operation method of an air conditioner which comprises a compressor, a condenser, an expansion device and an evaporator and supplies cold water through water pipes connected to the evaporator and operates a plurality of chillers connected the water pipes in parallel, wherein the operation method comprises steps of: setting a cold water set temperature if the pressure difference between the high pressure part and the low pressure part of the operating chiller is more than the set pressure for the set time; and controlling compressor capacity according to the cold water set temperature set at the step of setting a cold water set temperature; and transmitting an operation order to non operating chiller if the pressure difference is more than the set pressure for set time and at least one of the chillers is not operating until the present.

In the step of setting the cold water set temperature, if the pressure difference is more than the set pressure for the set time, the cold water set temperature may rise.

In the step of transmitting the operation order, the operation order and the stop set temperature of the chiller not operating until the present may be transmitted together to the non-operating chiller.

After the step of transmitting the operation order, if the cold-water exit temperature of a common water pipe of all water pipes is different with the water set temperature, it may return to the step of setting the cold water set temperature.

The operation method of an air conditioner further comprises steps of increasing the cold water set temperature if the cold water exit temperature of a common water pip of all the water pipes is lower than the cold water set temperature after the step of transmitting the operation order; and re-controlling the capacity of the compressor according to the cold water set temperature set in the step of the increasing the cold water set temperature.

The operation method of an air conditioner further comprises a step of stopping the operating chiller if the cold water set temperature is higher than the stop set temperature of the chiller after the step of re-controlling the compressor capacity.

The operation method of an air conditioner further comprises steps of decreasing the cold water set temperature if the cold water exit temperature of a common water pipe of all the water pipes is higher than the cold water temperature after the step of transmitting the operation order; and re-controlling the compressor capacity according to the cold water set temperature set in the step of the decreasing the cold water set temperature.

After the step of re-controlling the compressor capacity, it may return to the step of setting the cold water set temperature.

Advantageous Effects

According to the present invention as stated above, it controls the compressor capacity according to the cold water set temperature, so that it is possible to operate efficiently according to the load and to minimized power consumption.

In addition, it is possible to operate the least chiller in case of the partial load or to operate an additional chiller not operating until the present if one chiller is insufficient to act the load. Thus, it is possible to operate responding to a change of the load by using the minimum electric power.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of an air conditioner according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing the inside of an air-handling unit shown in FIG. 1.

FIG. 3 is a schematic diagram showing the inside of a chiller shown in FIG. 1.

FIG. 4 is a block diagram of an air conditioner according to the present invention.

FIG. 5 is a flow chart showing an operation method of an air conditioner according to the exemplary embodiment of the present invention.

BEST MODE

The present invention will hereinafter be described in detail with reference to the accompanying drawings in which exemplary embodiments of the invention are shown.

FIG. 1 is a schematic diagram of an air conditioner according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the inside of an air-handling unit shown in FIG. 1.

FIG. 3 is a schematic diagram showing the inside of a chiller shown in FIG. 1. FIG. 4 is a block diagram of an air conditioner according to the present invention.

Referring to FIG. 1, an air conditioner according to the exemplary embodiment of the present invention comprises at least one air-handling unit 1, 2 and a plurality of chillers 3, 4 and 5. At least one air-handling unit 1, 2 and a plurality of chillers 3, 4 and 5 are connected by a water pipe.

The air-handling units 1, 2 are demand spaces in which the cold water supplied from the plurality of the chillers 3, 4 and 5 is used. The air-handling units 1, 2 include a heat exchanger such as a coil, which the cold water supplied from the plurality of the chillers 3, 4 and 5 passed through.

The air-handling units 1, 2 may comprise a non-ventilation air conditioning unit which heat-exchanges the indoor air in the heat exchanger and then supplies the heat-exchanged air to the room, or may comprise a ventilation air conditioning unit which mixes the indoor air with the outdoor air and heat-exchanges the mixed air in the heat exchanger and then supplies to the heat-exchanged air to the room. Hereinafter, it is described that the air-handling units 1, 2 are comprise the ventilation air conditioning unit.

The air-handling units 1 and 2 may be installed in the air conditioning room or the machine room, which is apart from the room that the air-handling units 1 and 2 in the building including the air conditioner perform the air conditioning. In addition, the air-handling units 1 and 2 may be installed in the outside.

The air-handling units 1 and 2 may be comprise a plurality of units such as the chillers 3, 4 and 5 or may be comprise one unit so that the cold water supplied from the plurality of the chillers 3, 4 and 5 are being gathered and passed through.

If the air-handling units 1 and 2 comprise a plurality of units, it is possible that each of the air-handling units perform the air conditioning of the separate rooms or the air conditioning of the one room.

The chillers 3, 4 and 5 are a cold water supply unit for supplying the cold water to the air-handling unit 1 and 2 by using the refrigeration cycle, which comprises a compressor, a condenser, an expansion device and an evaporator.

The chillers 3, 4 and 5 may be installed in the outside in case of air-cooling condenser. Also, the chillers 3, 4 and 5 may be installed in the machine room such as the basement or the outside in case of water-cooling condenser.

The water pipes 6 include a common water pipe 7, a chiller connection water pipe 8, 9 and 10, and an air-handling unit connection pipe 11 and 12.

All the cold water supplied from each of the chillers 3, 4 and 5 passed through the common water pipe 7 of the water pipes 6.

The chiller connection water pipes 8, 9 and 10 connect the common water pipe 7 with the plurality of the chillers 3, 4 and 5.

The air-handling unit connection water pipes 11 and 12 connect the common water pipe 7 with at least one of the air-handling units 1 and 2.

The water pipes 6 comprise a supply water pipe for supplying the cold water of the chillers 3, 4 and 5 to the air-handling units 1 and 2 and a collect water pipe for collecting the cold water passed through the air-handling units 1 and 2 to the chillers 3, 4 and 5.

The air-handling units 1 and 2 include a fan, which inhales the indoor air and the outdoor air and blows the air inhaled to the heat exchanger and supplies the air passed through the heat exchanger to the room, and an air-handling unit controllers 13 and 14 for controlling the fan, etc.

If the air-handling units 1 and 2 are a plurality of units, the air-handling unit controllers 13 and 14 of each the air-handling unit 1 and 2 are connected by a communication line 15 each other.

The plurality of the chillers 3, 4 and 5 includes chiller controllers 16, 17 and 18 for controlling the compressor.

A chiller controller 16 of the plurality of the chiller controllers 16, 17 and 18 is connected with the air-handling unit controller 13 of the air-handling units 1 and 2 by a communication line 19. The communication line 20 and 21 connects each of the chiller controllers 16, 17 and 18 so that one of the chillers 3, 4 and 5 can transmit an operation order to the other chiller

For example, if the air-handling units 1 and 2 comprise a first air-handling unit 1 and a second air-handling unit 2. And if the chillers 3, 4 and 5 comprise a first chiller 3, a second chiller 4 and a third chiller 5. Each of air-handling unit controllers 13 and 14 of the first air-handling unit 1 and the second air-handling unit 2 is connected by the communication line 15.

Any one air-handling unit controller 13 of the first air-handling unit 1 and the second air-handling unit 2 is connected with the chiller controller 16 of the first chiller 3 by the communication line 19. The chiller controller 16 of the first chiller 3 and the chiller controller 17 of the second chiller 4 are connected by the communication line 20 so that the first chiller 3 can input an operation order to the second chiller 4. The chiller controller 17 of the second chiller 4 and the chiller controller 18 of the third chiller 5 are connected by the communication line 21 so that the second chiller 4 can input an operation order to the third chiller 5.

Hereinafter, one of the air-handling units 1 and 2 will be described in detail with reference to FIG. 2.

The air-handling units 1 and 2 include an air-handling unit case 22, which has a space on the inside and comprises an indoor air intake part 22A, and an indoor air discharge part 22B, and an outdoor air intake part 22C, and an air-conditioned air discharge part 22D.

The air-handling units 1 and 2 further comprise fans 27 and 28, which are disposed in the air-handling unit case 22 and make the indoor air and the outdoor air flow, and a heat exchanger 40 disposed in the air-handling unit case 22 and heat-exchanges the air flowing to the air-conditioned air discharge part with the cold water.

The air-handling units 1 and 2 are connect with a ventilation duct 22E which connects the indoor and the indoor air intake part 22A for inhaling indoor air into the air-handling unit case 22 through the indoor air intake part 22A.

The air-handling units 1 and 2 are connected with an exhaust duct 22F which connects the outdoor and the indoor air discharge part 22B for discharging some of the air inhaled into the air-handling unit case 22 through the indoor air intake part 22A to the outdoor.

The air-handling units 1 and 2 are connected with an outdoor air duct 22G which connects the outdoor and the outdoor air intake part 22C for inhaling the outdoor air into the air-handling unit case 22 through the outdoor air intake part 22C.

The air-handling units 1 and 2 are connected with an air supply duct 22H which connects the air-conditioned air discharge part 22D and the indoor for supplying the air-conditioned air of the air-handling unit case 22 to the indoor.

The ventilation duct 22E connects to the indoor air intake part 22A, and the exhaust duct 22F connects to the indoor air discharge part 22B, and the outdoor air duct 22G connects to the outdoor air intake part 22C, and the air supply duct 22H connects the air-conditioned air discharge part 22D.

In the air-handling units 1 and 2, some of the indoor air inhaled to the indoor air intake part 22A discharge to the outdoor through the indoor air discharge part 22B, and the rest mixes with the outdoor air inhaled to the outdoor air intake part 22C, and the mixed air heat-exchanges with the heat exchanger 40 and supplies to the indoor through the air-conditioned air discharge part 22D and the air supply duct 22H.

In the air-handling units 1 and 2, a mixing chamber 26 for mixing the indoor air with the outdoor air is disposed at the front of the heat exchanger 40 in the air flow direction.

The fans 27 and 28 comprise a return fan 27, which is disposed at the space between the indoor air intake part 22A and the indoor air discharge part 22B in the air flow direction and inhales the indoor air into the air-handling unit case 22 and blows the air inhaled, and a supply fan 28, which is disposed at the space between the heat exchanger 40 and the air-conditioned air discharge part 22D in the air flow direction and inhales the mixed air into the heat exchanger 40 and blows the air inhaled to the air-conditioned air discharge part 22D.

The fans 27 and 28 comprise a variable air volume fan to control air volume.

The fans 27 and 28 comprise a blower 29, and a housing 32 which surrounds the blower 29 and includes an air inlet 30 and an air outlet 31, and a blower driver 33 for rotating the blower 29.

The blower driver 33 may comprise a motor that a rotary shaft connects to the center of rotation of the blower 29. Also, The blower driver 33 may comprise a shaft 34 connected to the center of rotation of the blower 29, and a motor 35 disposed at the outside of the housing 32, and a power transmission device for transmitting a driving power of the motor 35 to the shaft 34.

The power transmission device may comprise a driving pulley 36 disposed at the shaft of the motor 35, and a driven pulley 38 disposed at the shaft 34, and a belt 37 wrapped around the driving pulley 35 and the driven pulley 38.

The motor 35 may comprise an inverter motor to change rpm of the blower 29.

The heat exchanger 40 is a kind of cooling coil for cooling the mixed air by heat exchange the mixed air and cold water and includes a cold-water coil having a flow path which cold water passes through.

The heat exchanger 40 is disposed at the space between the mixing chamber 26 and the supply fan 27 and connects with the air-handling unit connection pipes 11 and 12 of the water pipes 6.

The air-handling units 1 and 2 are further comprise dampers 43, 44 and 45 which can control the ratio of the indoor air to the outdoor air in the mixed air.

The dampers 43, 44 and 45 comprise a exhaust damper 43 which is disposed at the indoor air discharge part 22B and controls the discharge amount of the indoor air, and a outdoor air damper 44 which is disposed at the outdoor air intake part 22C and controls the intake amount of the outdoor air, and a mixture damper 45 which is disposed at the mixing chamber 26 and controls the amount of the air being inhaled into the mixing chamber 26.

Hereinafter, one of the chillers 3, 4 and 5 will be described in detail with reference to FIG. 3.

The chillers 3, 4 and 5 comprise a chiller case 50, and a compressor 51 for compressing refrigerant, and a condenser 52 for condensing the refrigerant compressed in the compressor 51, and an expansion device 53 for expanding the refrigerant condensed in the condenser 52, and an evaporator 54 for evaporating the refrigerant expanded in the expansion device 53 by heat-exchanging the expanded refrigerant with water.

The chillers 3, 4 and 5 forms of refrigerant cycle by the compressor 51, the condenser 52, and the expansion device 53, and the evaporator 54.

If the condenser 52 is an air-cooling type, the chillers 3, 4 and 5 may be installed in the outside. In addition, if the condenser 52 is a water-cooling type, the chillers 3, 4 and 5 may be installed in the machine room such as the basement or the outside.

The compressor 52, the condenser 52, the expansion device 53, and the evaporator 54 are disposed in the chiller case 50. If the condenser 52 is an air-cooling type, the outdoor air is inhaled into the chiller case 50 and heat-exchanged with the condenser 52 and then is discharged to the outside of the chiller case 50.

The compressor 51 comprises a variable capacity compressor for changing a capacity. It is possible to drive some or all the compressors according to the load. In addition, it is possible to use an inverter compressor for changing a frequency according to the load.

A discharge pipe of the compressor 51 connects to the condenser 52. An oil separator 55 is disposed at the discharge pipe of the compressor 51 for separating the refrigerant discharged from the compressor 51 into refrigerant and oil. The oil separator 55 connects with an oil collection path 56 for returning the oil to the compressor 51.

The condenser 52 may condense refrigerant by the outdoor air sent by the outdoor fan 57 or may condense refrigerant by the cold water supplied from a cooling tower (not shown). Hereinafter, it is described that the outdoor air sent by the outdoor fan 57 condenses the refrigerant.

The evaporator 54 connects with the heat exchanger 40 of the air-handling units 1, 2 and the water pipe 6 and is a kind of a cooler for cooling water by evaporation of the refrigerant expanded from the expansion device 53.

In the evaporator 54, a heat-exchanger part is sandwiched in between a refrigerant path for passing refrigerant and a water path for passing water.

The evaporator 54 comprises a plurality of inner tubes which form the water path for passing water, and a shell-tube type heat exchanger which is disposed at the outside of the inner tubes and includes a shell. The shell includes refrigerant tube, which is disposed at the space among the inner tubes for passing refrigerant.

The plurality of inner tubes of the evaporator 54 connects with the chiller connection pipes 8, 9 and 10.

The water pipe 6 is disposed to pass through each the chiller case 50 and the air-handling unit case 22. A cold-water pump 58 is installed at the water pipe 6 for pumping and circulating the cold water.

It is possible that the cold water pump 58 is installed at a position of the water pipe 6 located at the inside of the air-handling units 1 and 2 or is installed at a position of the water pipe 6 located at the inside of the chillers 3, 4 and 5 or is installed at a position of the water pipe located at the space between the air-handling units 1, 2 and the chillers 3, 4 and 5.

It is desirable that the cold-water pump 58 is installed at the inside of the air-handling units 1, 2 or the inside of the chillers 3, 4 and 5 to easy to connect an electric wire or to control that.

In the chillers 3, 4 and 5, the temperature of cold water discharged from the evaporator 54 depends on the capacity of the compressor 51. The capacity of the compressor 51 is controlled by the cold water set temperature Twt.

The chillers 3, 4 and 5 set a cold-water set temperature Twt of the operating chiller according to the pressure difference between the high-pressure side and the low-pressure side of the operating chiller.

The chillers 3, 4 and 5 further comprise a low-pressure sensor 59 for sensing suction pressure of the compressor 51, and a high-pressure sensor 60 for sensing discharge pressure of the compressor 51. The chiller controller 16, 17 and 18 set a cold water set temperature Twt according to the pressure difference between the high pressure sensed by the high pressure sensor 60 and the low pressure sensed by the low pressure sensor 59, and controls the capacity of the compressor 51 according to the cold water set temperature Twt.

The low-pressure sensor 59 is installed at the intake pipe connected for inhaling refrigerant into the compressor 51. The high-pressure sensor 60 is installed at the discharge pipe for passing the refrigerant discharged from the compressor 51.

The chiller controllers 16, 17 and 18 set the cold water set temperature Twt in the range of the lower limit Twtmin to the upper limit Twtmax so that the cold water temperature is variable in the range.

In the beginning of operation of the air conditioner, the chiller controllers 16, 17 and 18 control the compressor 51 by a standard capacity to respond to the standard cold water set temperature in the variable range of the cold water set temperature. Then, the chiller controllers 16, 17 and 18 set a new cold water set temperature Twt according to the pressure difference sensed by the low pressure sensor 59 and the high pressure sensor 60, and drive the compressor 51 by a new capacity which is responding to the new cold water set temperature Twt.

When the chillers 3, 4 and 5 the cold water set temperature Twt as stated above, if the pressure difference between the high pressure and the lower pressure is more than the set pressure for the set time, the chillers operating until the present is impossible to respond to the load. Thus, the chillers 3, 4 and 5 raise the cold water set temperature Twt to decrease the power consumption of the operating chiller and transmit an operation order to the non-operating chiller if there is a chiller not operating until the present.

Referring to FIG. 1, the air conditioner according to the exemplary embodiment of the present invention further comprises a common water pipe temperature sensor 62 for sensing temperature of the common water pipe 7 of the water pipes 6, and a controller 64 for controlling an operation or stop the air conditioner and for inputting a demand temperature such as the indoor set temperature.

The common water pipe temperature sensor 62 senses temperature of the cold water being supplied to the air-handling units 1 and 2 from the chillers 3, 4 and 5 and is installed at the common water pipe 7 of the supply water pipe.

The chiller controllers 16, 17 and 18 operate or stop the chillers 3, 4 and 5 according to the input of the controller 64. In addition, the chiller controllers 16, 17 and 18 newly set a cold-water set temperature Twt according to the pressure sensed by the high-pressure sensor 60 and the low-pressure sensor 59 and operate the chiller not operating until the present. Then, the chiller controllers 16, 17 and 18 newly set a cold water set temperature Twt according to the temperature of cold water sensed by the common water pipe temperature sensor 62 and control the capacity of the compressor according to the new cold water set temperature Twt.

An operation of the present invention will hereinafter be described in detail.

If a user operates the air conditioner by the controller 64, the air-handling units 1 and 2 is operated and at least one of the chillers 3, 4 and 5 is operated.

In the chillers 3, 4 and 5, the chiller controllers 16, 17 and 18 of the operating chiller drives an outdoor fan 57 and the compressor 51, controls the opening of the expansion device 53, and drives the cold-water pump 58.

While the compressor 52 is operated, refrigerant is circulated through the compressor 51, the condenser 52, the expansion device 53 and the evaporator 54. At this time, the refrigerant passing through the evaporator 53 takes the heat of water so that the temperature of water is decreased.

While the cold-water pump 58 is operated, the water chilled through the evaporator 54 cools down the heat exchanger 40 of the air-handling units 1 and 2 by passing through the water pipe 6 and then returns to the evaporator 54 by passing through the water pipe 6. At this time, water cools the heat exchanger 40 by circulating the evaporator 54 and the heat exchanger 40.

While the fans 27 and 28 are operated, the indoor air is inhaled to the inside of the air-handling unit case 22 through the ventilation duct 22E. Some of the inhaled air discharge to the outdoor through the exhaust duct 22F, the rest is inhaled to the mixing chamber 26. And the outdoor air is inhaled to the mixing chamber 26 through the outdoor air duct 22G and is mixed with some indoor air inhaled to the mixing chamber 26 of the indoor air. The mixed air passes through the heat exchanger 40 and loses the heat to the water passing through the heat exchanger 40. Thus, the temperature of the mixed air is decreased, and the air is supplied to the indoor through the air supply duct 22H.

While the air conditioner as stated above is operated, the chiller controller of the operating chiller determines the capacity of the compressor 52 according to the cold water set temperature and drives the compressor 51 according to the determined capacity and drives the non-operating chiller in case of need to use the non-operating chiller.

In the beginning of operation of the air conditioner, the chiller controllers 16, 17 and 18 set the cold water set temperature Twt by the standard cold water set temperature Twi in the range of the cold water set temperature and drive the compressor 51. Then, if a new cold-water set temperature Twt is set, the capacity of the compressor 51 is controlled according to the new cold water set temperature.

For example, if the variable range of the cold water set temperature Twt is set from 5° C. to 15° C., the standard cold water set temperature Twi is set 10° C. The chiller controller of the operating chiller controls the compressor 51 by a suitable capacity for the standard cold water set temperature. While the compressor is operated, the cold water set temperature is variable according to the difference of the high pressure and the low pressure and the temperature of the common water pipe 7. Since then, it controls the compressor 51 by a suitable capacity for the variable cold water set temperature.

Hereinafter, it is described an operation method of the air conditioner, wherein, when one chiller 3 of the chillers 3, 4 and 5 is operated, the operating chiller 3 changes the cold water set temperature Twt according to the difference of the high pressure and the low pressure and operates the other chiller 4 and changes the cold water set temperature Twt according to the temperature of the common water pipe 7.

FIG. 5 is a flow chart showing an operation method of an air conditioner according to the exemplary embodiment of the present invention.

An operation method of an air conditioner according to the exemplary embodiment of the present invention comprises the steps of setting the cold water set temperature (S1)(S2) and the step of controlling the compressor capacity (S3).

In the steps of setting the cold water set temperature, the cold water set temperature is set according to the pressure difference between the high pressure and the low pressure of the operating chiller 3. (S1)(S2)

In the steps of setting the cold water set temperature if the pressure difference is more than the set pressure for a set time (for example, 10 minutes), as follows, it is considered an operation of the chiller 4 not operating until the present, the cold water set temperature of the operating chiller 3 is raised so as to decrease the power consumption of the operating chiller 3. (S1)(S2),

In the steps of setting the cold water set temperature, if the high pressure and the low pressure are sensed immediately after the initial operation of the chiller 3, the standard cold water set temperature Twi is used to a cold water set temperature in the present, since then the temperature higher than the standard cold water set temperature Twi about a set value (for example, 0.5° C.) is used to a cold water set temperature. On the contrary to this, if the cold water set temperature is changed according to the sense of the high pressure and the low pressure, the cold water set temperature at the time sensed the high pressure and the low pressure is used to a cold water set temperature in the present, since then the temperature higher than the standard cold water set temperature Twi about a set value (for example, 0.5° C.) is used to a cold water set temperature. (S1)(S2)

Meanwhile, in the operation method of the air conditioner, if the pressure difference is not more than the set pressure for a set time, the previous cold water set temperature is maintained.

As the step of controlling the compressor capacity (S3) is a step for controlling the operation capacity of the compressor 51 according to the cold water set temperature Twt set in the step of setting the cold water set temperature (S1) (S2), if the pressure difference is more than the set pressure for a set time (for example, 10 minutes), the compressor 51 is controlled by the operation capacity suitable for the raised cold water set temperature.

Meanwhile, in the operation method of the air conditioner, if the pressure difference is not more than the set pressure for a set time, it is maintained that the compressor 51 is controlled by the operation capacity suitable for the previous cold water set temperature.

Meanwhile, in the operation method of the air conditioner, for the step of controlling the compressor capacity (S3) or since then, if there is a non-operating chiller 4, it is performed a step of transmitting an operation order to the non-operating chiller 4. (S4)(S5) If there is not a non-operating chiller, namely, if all the chillers is operating, it is not performed the step of transmitting an operation order (S4) (S5).

In the step of transmitting an operation order (S4) (S5), an operation order in company with a stop set temperature of the non-operating chiller 4 are transmitted to the non-operation chiller 4. The chiller 4 not operating until the present will be operated or stopped in addition to the operating chiller according to the stop set temperature and the operation order transmitted.

The chiller 4 received the operation order and the stop set temperature of the chiller drives the compressor 51 and the outdoor fan 57, controls the opening of the expansion device 53, drives the cold-water pump 58.

The amount of cold water passing through at least one of the air-handling units 1 and 2 is more than before the chiller 4 is operated in addition. The temperature of cold water supplied to the indoor from the air-handling units 1 and 2 is lower than before the chiller 4 is operated in addition, and the load of the indoor is gradually decreased.

While the air conditioner is operated as stated above, after the step of transmitting the operation order (S4)(S5) is performed, the chiller 3 set the cold water set temperature according to the cold water exit temperature of the common water pipe 7 of the water pipes 6.

After the step of transmitting the operation order (S4)(S5), if the cold water exit temperature of the common water pipe 7 of the water pipes 6 is equal to the cold water set temperature, it is returned to the step of setting the cold water set temperature (S1)(S2). Namely, as the chiller 4 is operated in addition, the temperature of the cold water is equal to the cold water set temperature. Therefore, it is not changed the cold water set temperature in addition, it returns to the step of setting the cold water set temperature (S1)(S2) for sensing the change of the load.

And, it further comprises a step of increasing the cold water set temperature (S7)(S8) for increasing the cold water set temperature if the cold water exit temperature of the common water pipe 7 of the water pipes 6 is lower than the cold water set temperature after the step of transmitting the operation order (S4)(S5); and a step of re-controlling the compressor capacity (S9) for controlling the operation capacity of the compressor 51 according to the cold water set temperature set by the step of increasing the cold water set temperature (S7)(S8).

Namely, if the cold water exit temperature of the common water pipe 7 is less than the cold water set temperature because cold water is much more supplied by the operation of the chiller not operated before, the cold water set temperature of the operating chiller 3 is decreased again for decreasing the power consumption and the compressor 51 is controlled accordingly.

Meanwhile, after the step of re-controlling the compressor capacity (S9), if the cold water set temperature is more than the stop set temperature (for example, 15° C.) of the chiller, it is further comprised a step of stopping the operating chiller. (S10)(S11).

It is desirable that the stop set temperature of the chiller is set to a maximum temperature in the variable range of the cold water set temperature Twt of the operating chiller.

After the step of the transmitting the operation order (S4) (S5), if the cold water exit temperature of the common water pipe 7 of the water pipes 6 is more than the cold water set temperature, it is further comprised a step of decreasing the cold water set temperature (S12); and a step of re-controlling the compressor capacity (S13) according to the cold water set temperature set by the step of decreasing the cold water set temperature (S12).

Namely, even if the cold water is much more supplied by the operation of the chiller 4 not operated before, if the cold-water exit temperature of the common water pipe 7 is higher than the cold water set temperature, it means that the cold water is not sufficiently supplied from the operating chiller 3. Thus, it needs to decrease the cold water set temperature and to control the capacity of the compressor 51.

Meanwhile, in the operation method of the air conditioner, it returns to the step of setting the cold water set temperature (S1) (S2) after the step of re-controlling the compressor capacity. 

1. An air conditioner comprising: a plurality of chillers which include a compressor, a condenser, an expansion device and an evaporator and supply cold water through water pipes connected to the evaporator in parallel, wherein an operating chiller of the plurality of chillers sets a cold water set temperature of the operating chiller according to pressure difference between high pressure part and low pressure part and controls the compressor capacity according to the cold water set temperature and transmits an operation order to a chiller not operating until the present if the pressure difference is more than the set pressure for the set time and at least one of the chillers is not operating.
 2. The air conditioner of claim 1, wherein each of the chillers comprises a low pressure sensor for sensing suction pressure of the compressor; and a high pressure sensor for sensing discharge pressure of the compressor; and a chiller controller for setting a cold-water set temperature according to the pressure difference between the high pressure sensed by the high-pressure sensor and the low-pressure sensed by the low-pressure sensor, and for controlling the compressor capacity according to the cold water set temperature.
 3. The air conditioner of claim 2, further comprising a common water pipe temperature sensor for sensing temperature of a common water pipe which coolant supplied from the plurality of the chillers passes through together, wherein the chiller controller sets a cold-water set temperature according to the temperature sensed by the common water pipe temperature sensor.
 4. The air conditioner of claim 2, further comprising a communication line, which is connected to each the chiller controllers of the chillers for transmitting an operation order from one of the chillers to the other.
 5. An operation method of an air conditioner which comprises a compressor, a condenser, an expansion device and an evaporator and supplies cold water through the water pipes connected to the evaporator and operates a plurality of chillers connected the water pipes in parallel, wherein the operation method comprises steps of; setting a cold water set temperature if the pressure difference between the high pressure part and the low pressure part of the operating chiller is more than the set pressure for the set time; and controlling compressor capacity according to the cold water set temperature set at the step of setting a cold water set temperature; and transmitting an operation order to the non-operating chiller if the pressure difference is more than the set pressure for set time and at least one of the chillers is not operating until the present.
 6. The operation method of an air conditioner of claim 5, wherein, in the step of setting the cold water set temperature, if the pressure difference is more than the set pressure for the set time, the cold water set temperature is raised.
 7. The operation method of an air conditioner of claim 5, wherein, in the step of transmitting the operation order, the operation order and the stop set temperature of the chiller not operating until the present are transmitted together to the non-operating chiller.
 8. The operation method of an air conditioner of claim 5, wherein, after the step of transmitting the operation order, if the cold-water exit temperature of a common water pipe of all water pipes is different with the water set temperature, it returns to the step of setting the cold water set temperature.
 9. The operation method of an air conditioner of claim 5, further comprising steps of; increasing the cold water set temperature if the cold water exit temperature of a common water pip of all the water pipes is lower than the cold water set temperature after the step of transmitting the operation order; and re-controlling the capacity of the compressor according to the cold water set temperature set in the step of increasing the cold water set temperature.
 10. The operation method of an air conditioner of claim 9, further comprising a step of; stopping the operating chiller if the cold water set temperature is higher than the stop set temperature of the chiller after the step of re-controlling the compressor capacity.
 11. The operation method of an air conditioner of claim 10, further comprising steps of; decreasing the cold water set temperature if the cold water exit temperature of a common water pipe of all the water pipes is higher than the cold water temperature after the step of transmitting the operation order; and re-controlling the compressor capacity according to the cold water set temperature set in the step of decreasing the cold water set temperature.
 12. The operation method of an air conditioner of claim 11, wherein, after the step of re-controlling the compressor capacity, it returns to the step of setting the cold water set temperature.
 13. The air conditioner of claim 3, further comprising a communication line, which is connected to each the chiller controllers of the chillers for transmitting an operation order from one of the chillers to the other. 